The present invention relates to the field of semiconductor devices and their manufacture. More specifically, in one embodiment the invention provides a Schottky barrier diode formed using a single polysilicon layer process.
Schottky barrier diodes (SBD) or "Schottky diodes" are known particularly for their low voltage drop and rapid switching ability. Schottky barrier diodes are often used for clamping bipolar transistors to form a Schottky-clamped transistor, as described, generally, in U.S. Pat. No. 3,790,817 issued Feb. 5, 1974 to Dobkin. Methods of making Schottky diodes using a polysilicon/metal-silicide process have, in the past, involved doping the polysilicon and contacting metal directly with N-doped polysilicon as described in U.S. Pat. No. 4,908,679 issued Mar. 13, 1990 to Vora, et al., or opening a window in a polysilicon layer to permit contact of metal or metal silicide directly with an N-conductivity type epitaxial layer. Such previous methods have required the inclusion of multiple processing steps used in the formation of such diodes. For example, in order to open a window in a polysilicon layer, a mask is formed and an etching step must be conducted. Furthermore, because each window requires an edge or overlap area, in addition to the window area, previous methods for forming Schottky diodes occupied a relatively large surface area of an integrated circuit.
It has also been found that in previous Schottky diodes formed using a polysilicon process, the Schottky diode junction was often found to be shallow or degraded in certain regions causing localized areas of enhanced diffusion resulting in junction spiking.
Accordingly, there is a need for providing a Schottky diode which occupies a relatively smaller portion of an integrated circuit surface area, which requires fewer process steps, which is less susceptible to junction spiking, and which is more manufacturable compared to previous Schottky diode devices formed in integrated circuits using a polysilicon process.